1. Field of the Invention
The present invention relates to a vibration and sway preventing apparatus for suspended loads in container cranes or the like.
2. Description of the Prior Art
FIG. 4 shows a sway preventing apparatus for suspended loads in a conventional container crane. In FIG. 4, reference numeral 1 denotes a structural body of the crane, reference numeral 2 denotes a trolley that horizontally moves on the structural body 1 (left and right direction in FIG. 4), reference numeral 3 denotes a trolley drive device for horizontally driving the trolley 2, reference numeral 4 denotes drive ropes for tugging the trolley 2, reference numeral 5 denotes a horizontal drum rotated by the trolley drive device 3 for winding the drive rope 4, and reference numeral 6 denotes a suspended load to be delivered.
First of all, an explanation will be made as to the swaying of the suspended load. In the case where the trolley 2 is moved laterally or horizontally from left to right in the condition shown in FIG. 4, when the trolley 2 is accelerated, the suspended load 6 is moved to the left side of FIG. 4 by an inertia force. Then, after the trolley 2 has been moved through a predetermined distance, when the trolley 2 is decelerated, the suspended load 6 is swung forwardly at the right side in FIG. 4 by the inertia force unlike the acceleration of the suspended load 6. The conventional sway preventing apparatus copes with the problem of the swaying of the suspended load 6 as follows. A moving position of a mark 8 on a suspension tool 7 is recognized by an image sensor 9 mounted on a bottom surface of the trolley 2 so that a swaying shift and a swaying velocity of the suspended load 6 are detected. The position and the velocity of the trolley 2 are detected by a trolley position sensor 10 and a trolley velocity detector 11 provided in the trolley drive device 3. At the same time, swaying parameters (swaying shift and swaying velocity) of the suspended load 6 thus detected and motion parameters (trolley position and trolley velocity) of the trolley horizontal movement are input into a controller 12. On the basis of these motion parameters, the trolley velocity is calculated and a trolley velocity command is output to the trolley drive device 3.
As a result, the trolley drive device 3 is driven in accordance with the trolley velocity command, so that the sway preventing control is carried out for the suspended load 6. FIG. 5 is a block diagram showing a process for these steps.
As described above, in the conventional suspended load sway preventing apparatus, the trolley velocity is calculated from the suspended load swaying motion parameters and the motion parameters of the trolley horizontal movement so that the swaying preventing control of the suspended load 6 is carried out. However, there is no control to prevent vibration of the structural body 1, generated in accordance with the horizontal movement of the trolley 2.
The lateral movement of the trolley 2 also causes the structural body 1 to vibrate in addition to the swaying of the suspended load 6. The vibration of the structural body 1 will be explained. In the case where the trolley 2 is moved from left to right, the trolley drive device 3 tugs the trolley 2 in the right direction by driving the horizontal drum 5 in the direction in which the drive ropes 4 are wound. Then, a tension of each drive rope 4 on the right side is increased by the inertia force of the trolley 2 which tends to stop. On the other hand, the tension of the drive rope 4 on the left side is kept constant by each rope tensioner 13. For this reason, a tension difference is generated between the right and left sides of the drive rope 4. This tension difference is applied through the horizontal drum 5 to the trolley drive device 3 fixed to the structural body 1, so that the structural body 1 is tensed to the right on the high tension side and is twisted to the right. As a result, a natural frequency of the structural body 1 is excited to generate the vibration.
Then, in the case where the trolley 2 is stopped, the rotational speed of the horizontal drum 5 is decreased. However, since the trolley 2 tends to continue the horizontal movement in the right direction by the inertia force, the tension of the drive rope 4 on the right side is decreased. On the other hand, the tension of the drive rope 4 on the left side is kept constant by the rope tensioner 13. For this reason, a tension difference is generated on the opposite side to that generated during the acceleration as described above. By the tension difference, the structural body 1 is tugged on the left side where the tension is stronger. The body 1 is twisted in the left side. A natural frequency of the structural body 1 is excited to generate the vibration.
As described above, in the conventional suspended load sway preventing apparatus, since the vibration control is not applied to the vibration of the structural body 1, the conventional apparatus suffers from the following problems:
(1) The natural frequency cycle of vibration of the structural body 1 is short so that vibratory shift is small but the acceleration is large. Thus, the driver of the trolley is impressed with an unsatisfactory feeling.
(2) At some timing of the horizontal acceleration/deceleration of the trolley 2, the vibration of the structural body is amplified. Accordingly, there is a problem with respect to the fatigue strength of the structural body.